Elastically deformable support for an expandable seal element of a downhole tool

ABSTRACT

An elastically deformable support for an expandable seal element of a downhole tool, an expandable seal assembly incorporating such a seal element and support, and a downhole tool, such as a packer, incorporating the expandable seal assembly are disclosed. The elastically deformable support may be one-piece. The support is deformable between an unexpanded configuration and a radially expanded configuration and includes a plurality of base portions, each base portion having a surface which, in use, faces towards the seal element; and a plurality of overlap portions, each overlap portion extending from a respective base portion so that it overlaps the surface of an adjacent base portion and having a surface which, in use, faces towards the seal element. The base portions and the overlap portions are arranged to define a generally ring-shaped seal support structure which forms a continuous circumferentially extending support surface for abutting and supporting the seal element.

The present invention relates to an elastically deformable support foran expandable seal element of a downhole tool, and to an expandable sealassembly incorporating such a seal element and support. In particular,but not exclusively, the present invention relates to an elasticallydeformable support for an expandable seal element of a downhole toolsuch as a packer. The present invention also relates to a downhole tool,such as a packer, incorporating the expandable seal assembly.

In the oil and gas exploration and production industry, wellbore fluidscomprising oil and/or gas are recovered to surface through a wellborewhich is drilled from surface. The wellbore is lined with metalwellbore-lining tubing, which is known in the industry as ‘casing’. Thecasing serves numerous purposes, including: supporting the drilled rockformations; preventing undesired ingress/egress of fluid; and providinga pathway through which further tubing and downhole tools can pass.

There are three main phases involved in bringing a well into production.The first is the drilling phase, in which the wellbore is drilled fromsurface and the wellbore-lining tubing installed and cemented in place.The second is the completion phase, in which the well is prepared forproduction by cleaning the wellbore and installing production tubingextending to surface, through which well fluids are recovered. The thirdis the production phase, in which well fluids are recovered to surfacethrough the production tubing; this typically involves perforating thewellbore-lining tubing to allow the well fluids to enter the wellboreand flow into the production tubing.

During the lifetime of a well, it may be necessary to carry out anintervention procedure, in which production is halted and downhole toolsand/or tubing run into the well to perform a required function. Examplesof intervention activities include stimulating production by injectingwater or chemicals into the producing rock formation; operating adownhole valve to close or open flow from a particular zone; andinserting a straddle to bridge across a deteriorated or corroded sectionof the wellbore-lining tubing.

During these various phases and subsequent intervention procedures, itis frequently necessary to seal an annular region around tubing and/ortools located in the well. This is achieved using a dedicated deviceknown as a ‘packer’. The packer includes an expandable seal element of amaterial having a relatively low modulus of elasticity, and which istypically of a suitable elastomeric material. The seal element ismounted on a tubular mandrel of the packer, and is compressed byapplying an axially directed force on the seal element. This expands theseal element radially outwardly, to bridge the radial gap between thepacker mandrel and an internal surface of the tubing in which the packeris located, or conceivably against the wall of the drilled wellbore.

Conventional packer seal elements have a main or central portion whichis of a relatively low modulus of elasticity, the central portionperforming the primary seal function when the seal element is radiallyexpanded. The material adjacent the axial ends of the seal elements isof a higher modulus of elasticity than that of the central portion, toresist axial extrusion of the seal element under load. So-called ‘gartersprings’ are moulded into the axial ends of the seal element. Theseconsist of an outer helical spring wound in a first direction, and aninner helical spring wound in a second direction and located within theouter spring. The garter springs perform two main functions. The firstis to provide additional stiffness, in an effort to resist axialextrusion of the relatively soft central portion of the seal elementalong the wellbore, which can lead to seal failure. The second is toprovide an elastic restoring force, to facilitate return movement of theseal element to an unexpanded configuration when the packer is to beremoved from the wellbore.

Packer seal elements of this type suffer from a number of disadvantages.Chief amongst these is that, when the seal element is expanded, thegarter springs are expanded, opening up the spring coils. Theelastomeric material forming the seal element has a tendency to extrudeinto the spring coils, and can hamper retraction of the seal element. Inaddition, the inner and outer springs, although wound in oppositedirections, can still become entangled and so again hamper retraction.Another significant disadvantage is that the relatively soft materialforming the bulk of the seal element, which bridges the radial gap,still has a tendency to extrude axially along the wellbore under thehigh fluid pressure forces which the packers experience during use. Thiscan lead to packer failure, and so fluid migration past the packer sealelement, and can also further hamper retraction. Indeed, in extremecases, the packer can become lodged in the wellbore, requiring thepacker to be drilled or milled out, for example using an overshot toolwhich passes around the packer and mills away the seal element.

It is amongst the objects of the present invention to obviate ormitigate at least one of the foregoing disadvantages.

According to a first aspect of the present invention, there is provideda one-piece elastically deformable support for an expandable sealelement of a downhole tool, in which the support is deformable betweenan unexpanded configuration and a radially expanded configuration andcomprises:

-   -   a plurality of base portions, each base portion having a surface        which, in use, faces towards the seal element; and    -   a plurality of overlap portions, each overlap portion extending        from a respective base portion so that it overlaps the surface        of an adjacent base portion and having a surface which, in use,        faces towards the seal element;    -   in which the base portions and the overlap portions are arranged        to define a generally ring-shaped seal support structure which        forms a continuous circumferentially extending support surface        for abutting and supporting the seal element.

The base portions may be arranged so that they can separate tofacilitate expansion of the support. The overlap portions may bearranged so that they can slide over the surface of the adjacent baseportion during expansion of the support. In the expanded configurationof the support, the continuous circumferentially extending supportsurface may comprise the surfaces of the overlap portions and at leastpart of the surfaces of at least some of the base portions.

The overlap portions may function as anti-extrusion members, which termmay be used interchangeably with the term overlap portion.

According to a second aspect of the present invention, there is providedan elastically deformable support for an expandable seal element of adownhole tool, in which the support is deformable between an unexpandedconfiguration and a radially expanded configuration and comprises:

-   -   a plurality of base portions, each base portion having a surface        which, in use, faces towards the seal element; and    -   a plurality of overlap portions, each overlap portion extending        from a respective base portion so that it overlaps the surface        of an adjacent base portion and having a surface which, in use,        faces towards the seal element;    -   in which the base portions and the overlap portions are arranged        to define a generally ring-shaped seal support structure which        forms a continuous circumferentially extending support surface        for abutting and supporting the seal element;    -   in which the base portions are arranged so that they can        separate to facilitate expansion of the support;    -   in which the overlap portions are arranged so that they can        slide over the surface of the adjacent base portion during        expansion of the support;    -   and in which, in the expanded configuration of the support, the        continuous circumferentially extending support surface comprises        the surfaces of the overlap portions and at least part of the        surfaces of at least some of the base portions.

The deformable support of the present invention provides numerousadvantages over prior supports. These include the following. One-piececonstruction means that the support is effectively a single piececomponent. This provides clear benefits over complex prior supportscomprising numerous components (particularly to form a support surface),such as segments, petals or the like, in combination with supportsprings, screws etc. The present invention can provide good support fora seal element, and is significantly less complex and more reliable. Thecontinuous circumferentially extending support surface restrictsextrusion of the seal element (which may be of a material having arelatively low modulus of elasticity) following expansion of the supportand the seal element. In particular, where the support is arranged toabut and support a seal element provided at an axial end of the support,the support may restrict axial extrusion of the seal element. Also, asthe overlap portions extend from a respective base portion, the overlapportions may effectively separate when the support is expanded(facilitated by separation of the base portions). This may help toensure that expansion of the support occurs in a smooth and predictablefashion and may also make the support less complex and easier tomanufacture than prior supports. Furthermore, the arrangement wherebythe base portions separate (typically circumferentially) to facilitateexpansion of the support, and whereby the overlap portions slide overthe surface of the adjacent base portion, may be such that at least onedimension of the seal support structure, and so of the support surface,is maintained during expansion of the support. In particular, a radialdimension of the seal support structure (typically a radial width orheight), and so of the support surface, may be maintained. This mayprovide good support for the seal element, and may help to restrict orprevent extrusion of the seal element past the support followingexpansion of the support and the seal element.

In the unexpanded configuration of the support, the continuouscircumferentially extending support surface may comprise or may bedefined by the surfaces of the overlap portions.

In the unexpanded configuration of the support, the continuouscircumferentially extending support surface may comprise or may bedefined by the surfaces of the overlap portions and at least part of thesurfaces of at least some of the base portions. In this case, in theexpanded configuration of the support, the continuous circumferentiallyextending support surface may comprise the surfaces of the overlapportions and a greater proportion of the surfaces of said base portionsthan in the unexpanded configuration.

In the expanded configuration, the continuous circumferentiallyextending support surface may comprise the surfaces of the overlapportions and at least part of the surfaces of all of the base portions.

Each overlap portion may overlap the surface of a single adjacent baseportion.

At least one of the overlap portions may overlap the surface of morethan one adjacent base portion. At least one of the overlap portions mayextend from the respective base portion in opposed first and seconddirections, so that it overlaps base portions located adjacent first andsecond sides of the base portion from which the overlap portion extends.

At least one of the overlap portions may extend across and overlap theentire surface of the adjacent base portion. Said overlap portion mayextend over a surface of a further base portion.

Each overlap portion may extend in a generally circumferential directionfrom the respective base portion over the surface of the adjacent baseportion. The base portion which is overlapped by the overlap portion maybe one which is circumferentially adjacent.

The generally ring-shaped support structure may comprise a radiallyouter extent and a radially inner extent. The base portions may eachextend across a full radial width of the support structure, and so mayextend from the inner extent to the outer extent. The overlap portionsmay each extend across a full radial width of the support structure, andso may extend from the inner extent to the outer extent. The above maybe the case both when the support is in the unexpanded configuration andthe expanded configuration.

The base portions may form a base section of the generally ring-shapedseal support structure. In the unexpanded configuration of the support,the base portions may be arranged to form a ring-shaped base section.Each base portion may abut adjacent base portions in the unexpandedconfiguration. Expansion of the support may cause the base portions tomove out of abutment and so separate.

The overlap portions may form an overlap section of the generallyring-shaped seal support structure. In the unexpanded configuration ofthe support, the overlap portions may be arranged to form a ring-shapedoverlap section. Each overlap portion may abut adjacent overlap portionsin the unexpanded configuration. Expansion of the support may cause theoverlap portions to move out of abutment and slide over the adjacentbase portion.

The support surface may be for abutting and supporting an axial end ofthe seal element. The generally ring-shaped seal support structure maybe provided on, or may define, an axial end of the support. The supportsurface may therefore be an on axial end of the support. Advantageously,where the base portions and overlap portions extend across a full radialwidth of the support structure and are provided on or define the axialend of the support, this may provide good support for the seal elementand help to prevent extrusion of the seal element.

The support surface may be for abutting and supporting an inner surfaceof the seal element, which may be a radially inner surface. Thegenerally ring-shaped seal support structure may be provided on, or maydefine at least part of, an outer surface of the support, which may be aradially outer surface. The support surface may therefore be on aradially outer surface of the support.

The base portions may be spaced from the overlap portions, and may bespaced axially and/or radially. In use, the overlap portions may belocated closer to the seal element than the base portions.

The overlap portions may be provided integrally with their respectivebase portion. The overlap portions may be provided as separatecomponents which are attached to their respective base portion.

The base portions may be arranged so that they are generally in a firstplane which is perpendicular to a main axis of the support. The overlapportions may each extend out of the first plane to overlap the surfaceof the adjacent base portion. The overlap portions may be arranged sothat they are generally in a second plane which is parallel to the firstplane, and spaced axially along the support from the first plane. Thesecond plane may, in use, be disposed closer to the seal element thanthe first plane.

The overlap portions may have first and second circumferential edges.The overlap portions may be arranged to taper towards the edges, and/orthe edges may be tapered or chamfered. This may facilitate returnmovement of the support to the unexpanded configuration, in that it mayhelp to urge the seal element from an expanded configuration back to anunexpanded configuration and/or may prevent the seal element fromrestricting return movement of the support to its unexpandedconfiguration. The overlap portions may have a thickness or depth (in anaxial direction of the support), and the overlap portions may taper inthickness towards the edges.

The base portions may have radially outer and radially inner extents,and may taper from the outer extent to the inner extent. The baseportions may have first and second circumferential edges. The edges maybe inclined. The edges may be disposed parallel to a radius of thesupport, at least in the unexpanded configuration of the support. Thebase portions may have a greater width at the outer extent than at theinner extent. The base portions may be generally trapezoidal, forexample generally wedge-shaped.

The overlap portions may have radially outer and radially inner extents,and may taper from the outer extent to the inner extent. The overlapportions may have first and second circumferential edges. The edges maybe inclined. The edges may be disposed parallel to a radius of thesupport, at least in the unexpanded configuration of the support. Theoverlap portions may have a greater width at the outer extent than atthe inner extent. The overlap portions may be generally trapezoidal, forexample generally wedge-shaped.

The support may comprise first and second axially opposed ends. Thesupport may comprise a first generally ring-shaped seal supportstructure provided on the first axial end, and a second generallyring-shaped seal support structure provided on the second axial end. Thefirst generally ring-shaped seal support structure may be arranged toabut and support a first seal element at the first axial end of thesupport. The second generally ring-shaped seal support structure may bearranged to abut and support a second seal element at the second axialend of the support. Advantageously therefore, the support may be capableof abutting and supporting two separate, axially spaced seals. The firstand second generally ring-shaped seal support structures may eachcomprise respective base portions and overlap portions.

The base portions may each comprise a plurality of legs, arms or fingersextending in an axial direction of the support. The base portions mayeach comprise a pair of said legs. Where the support comprises a firstgenerally ring-shaped seal support structure provided on a first axialend of the support, and a second generally ring-shaped seal supportstructure provided on a second axial end, each leg of each base portionmay extend from the base portion to a different base portion on theother support structure.

The support may comprise a plurality of slots, channels or the like,each extending between an inner surface of the support and an outersurface of the support, and so which may extend through a wall of thesupport. Said slots may extend in an axial direction along thecomponent, and may be positioned so that their main axes are disposedgenerally parallel to a main longitudinal axis of the support. The slotsmay be expandable to facilitate expansion of the support with the sealelement. Advantageously, the seal support structure may effectivelycover ends of the slots, and so may help to prevent extrusion of theseal element into the slots, following expansion. In particular, wherethe base portions and overlap portions extend across a full radial widthof the support structure and are provided on or define the axial end ofthe support, the base and overlap portions may cover the ends of theslots.

Said slots may open when a force is exerted on the support to move it tothe expanded configuration. Said slots may have a width in a directionaround a perimeter of the support, which may be a circumferential width,and the width may increase when the support is moved to the expandedconfiguration. The support may therefore circumferentially expand whenit is moved to the expanded configuration. At least part of said slot,which may be a main part, may have a width which is substantiallyconstant when the component is in the unexpanded configuration. Saidslots may be arranged so that, on expansion of the support, the widthincreases and may then be non-constant in a direction along at leastsaid main part of the slot.

Said slots may extend inwardly from an axial end of the support part-wayalong a length of the support, and may terminate in an axially innerend, which may define an expansion node. Each said slot may have opposedsidewalls which extend from the axial end to the respective node, andexpansion may occur by at least part of each of said sidewalls pivotingor deflecting about the node. The sidewall may pivot or deflect in ascissors-fashion about the node. The node may effectively form a root ofthe slot, and expansion may occur by pivoting/deflecting of said part ofthe sidewalls from the root so that the sidewalls diverge in a directionaway from the root. Each node may have a wall which is curved, and whichmay have a substantially constant radius of curvature, the node wallcommunicating with the slot or channel sidewall. Providing a node wallwhich has such a substantially constant radius of curvature results inthe node being generally circular, which may reduce stressconcentrations under load.

The support may comprise first and second sets of slots or channels,each set comprising a plurality of slots or channels, said slots of thefirst set extending inwardly from a first axial end of the support, andsaid slots of the second set extending inwardly from a second axial endof the support opposite to the first end. Said slots of the first setmay axially overlap said slots of the second set. The slots or channelsof the first and second sets may be circumferentially spaced around thesupport. The slots or channels of the first set may be spacedalternately between slots or channels of the second set around thecircumference of the support.

The support may define a gripping arrangement, which may be for grippinga downhole surface. This may enable the support to act as a slip or setof slips. The gripping arrangement may be provided on or defined by aradially outer surface of the support. The gripping arrangement maycomprise a plurality of gripping elements, which may be protrusions suchas teeth. The gripping arrangement may be provided by arranging at leastpart of said outer surface to be roughened, and/or by applying a coatingto the part of said surface which is of a higher coefficient of frictionthan a material of the support (for example, a Tungsten Carbidecoating).

The support may comprise a seal component extending around at least partof a radially outer surface of the support. This may be for sealing thesupport relative to a downhole surface, following expansion. Where thesupport comprises a plurality of slots, this may provide the advantagesof: reducing junk ingress to the slots, causing it to not retract fully;and aiding return to the unexpanded configuration (i.e. to gauge OD), byincreasing the ‘memory’ of the support. The seal component may extend atleast partly into the slots.

The seal component may be a generally tubular sheath. The support may beencapsulated by the seal component.

The seal element may be mountable on or in the support surface, and sothe support may have an integral seal element. The seal element may bean annular seal element such as an O-ring (of any suitablecross-section), and may be located in a seat defined on or in thesupport surface. The support element may therefore define a retractableseal seat. The seal element may be provided on or in an axial end of thesupport, or a radially outer surface of the support. This feature of theinvention could have applications where a certain component needs topass and seal through a second component which has a restriction priorto a sealing area, which might be of a larger diameter. There are avariety of sealing systems available, which could utilise the presentinvention as a back-up/support.

The support may be tubular, and may be generally annular in shape. Thesupport may be configured so that it circumferentially expands when thesupport is moved to the expanded configuration.

According to a third aspect of the present invention, there is providedan expandable seal assembly for a downhole tool, the seal assemblycomprising:

-   -   an expandable seal element which is radially expandable between        an unexpanded configuration where the seal element is out of        contact with a downhole surface, and an expanded configuration        where the seal element can sealingly abut the downhole surface;        and    -   an elastically deformable support according to the first aspect        of the invention.

According to a fourth aspect of the present invention, there is providedan expandable seal assembly for a downhole tool, the seal assemblycomprising:

-   -   an expandable seal element which is radially expandable between        an unexpanded configuration where the seal element is out of        contact with a downhole surface, and an expanded configuration        where the seal element can sealingly abut the downhole surface;        and    -   an elastically deformable support for the expandable seal        element which is deformable between an unexpanded configuration        and a radially expanded configuration, the support comprising:    -   a plurality of base portions, each base portion having a surface        which faces towards the seal element; and    -   a plurality of overlap portions, each overlap portion extending        from a respective base portion so that it overlaps the surface        of an adjacent base portion and having a surface which faces        towards the seal element;    -   in which the base portions and the overlap portions are arranged        to define a generally ring-shaped seal support structure which        forms a continuous circumferentially extending support surface        for abutting and supporting the seal element;    -   in which the base portions are arranged so that they can        separate to facilitate expansion of the support;    -   in which the overlap portions are arranged so that they can        slide over the surface of the adjacent base portion during        expansion of the support;    -   and in which, in the expanded configuration of the support, the        continuous circumferentially extending support surface comprises        the surfaces of the overlap portions and at least part of the        surfaces of at least some of the base portions.

The support may comprise first and second axially opposed ends. The sealassembly may comprise first and second expandable seal elements. Thesupport may comprise a first generally ring-shaped seal supportstructure provided on the first axial end, and a second generallyring-shaped seal support structure provided on the second axial end. Thefirst generally ring-shaped seal support structure may be arranged toabut and support the first seal element, which may be provided at thefirst axial end of the support. The second generally ring-shaped sealsupport structure may be arranged to abut and support the second sealelement, which may be provided at the second axial end of the support.The first and second generally ring-shaped seal support structures mayeach comprise respective base portions and overlap portions.

The support may be high expansion, and so may be a high expansionsupport. Consequently the expandable seal assembly, and seal element,may be a high expansion assembly/element. A high expansion support mayhave a use where a tool of a certain diameter is to pass a restriction,and then to expand into a larger diameter area whilst sealing pressurefrom above and below. Such may involve a temporary (and so retractable)or permanent deployment. A ratio of an outer diameter of thesupport/seal element in the unexpanded configuration relative to anouter diameter in the expanded configuration may be at least about 1:1.2(representing at least a 20% expansion).

The seal assembly may comprise first and second supports and the/a sealelement may be disposed between the supports so that the first supportabuts and supports a first surface of the seal element, and the secondsupport abuts and supports a second, opposite surface of the sealelement. It will be understood that the assembly may be operable withone or more seal elements using one or more supports.

Reference is made to contact between the seal element and a downholesurface. It will be understood that the downhole surface may be asurface on any tubing or tool deployed downhole, or potentially the wallof a wellbore (in an open-hole sealing situation). Conceivably, the sealassembly can seal by contact with any downhole surface of a suitableshape.

The support may be of a material selected from the group comprisingmetals, metal alloys and plastics materials. The seal element may be ofan elastomeric or rubber material. The modulus of elasticity of thesupport may be in the range of around 180 GPa to around 200 GPa. Themodulus of elasticity of the seal element may be in the range of around0.01 GPa to around 0.1 GPa.

Further features of the support forming part of the seal assembly of thethird/fourth aspect of the invention are defined above in relation tothe first/second aspect of the invention.

According to a fifth aspect of the present invention, there is provideda downhole tool comprising at least one expandable seal assemblyaccording to the third/fourth aspect of the invention.

The downhole tool may be a packer, straddle, bridge plug or similarproducts. The downhole tool may comprise a plurality of said sealassemblies, which may be spaced axially along a length of the tool.

The at least one seal assembly may be mounted on a main body of thedownhole tool, and the downhole tool may comprise at least one actuationmember which is moveable relative to the main body to urge the sealassembly to the expanded configuration. The/each actuation member may beoperable to urge both the seal and support elements to their expandedconfigurations. The/each actuation member may comprise an expansionsurface arranged to urge both the elements to their expandedconfigurations. The/each actuation member may comprise a seal expansionsurface arranged to urge the seal element to its expanded configuration,and a support expansion surface arranged to urge the support element toits expanded configuration. The downhole tool may comprise a furtheractuation member, which may be fixedly or moveably mounted relative tothe main body of the tool, and the actuation members may cooperate tourge the seal assembly to the expanded configuration.

Further features of the seal support/assembly forming part of thedownhole tool of the fifth aspect of the invention are defined above inrelation to the first to fourth aspects of the invention.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic side view of a downhole tool, comprising at leastone expandable seal assembly incorporating an elastically deformablesupport for an expandable seal element of the assembly, according to anembodiment of the invention;

FIGS. 2 and 3 are enlarged perspective and side views, respectively, ofthe seal assembly of FIG. 1;

FIG. 4 is a side view which is similar to FIG. 3, but with the supportof the seal assembly shown in longitudinal cross-section;

FIGS. 5, 6 and 7 are views similar to FIGS. 2, 3, and 4, respectively,but showing the downhole tool following actuation, in which the sealassembly has been radially expanded;

FIG. 8 is a perspective view of the support forming part of the sealassembly of FIG. 1, shown prior to expansion, as in FIG. 2;

FIG. 9 is a perspective view of the support forming part of the sealassembly of FIG. 1, shown following expansion, as in FIG. 5;

FIGS. 10 and 11 are side views of the support in the configurations ofFIGS. 8 and 9, respectively;

FIG. 12 is a side view of downhole tool, comprising at least oneexpandable seal assembly incorporating an elastically deformable supportfor an expandable seal element of the assembly, according to anotherembodiment of the invention;

FIG. 13 is a side view of an elastically deformable support according toa further embodiment of the invention; and

FIGS. 14 and 15 are enlarged side and end views, respectively, of partof an elastically deformable support according to a still furtherembodiment of the invention.

Turning firstly to FIG. 1, there is shown a side view of a downhole toolcomprising at least one expandable seal assembly having an elasticallydeformable support, according to an embodiment of the invention. Thedownhole tool is indicated generally by reference numeral 10, theexpandable seal assembly by reference numeral 12, and the elasticallydeformable support by reference numeral 13. In the illustratedembodiment, the downhole tool 10 takes the form of a packer. The packer10 is shown coupled to a string of tubing 14, which has been located ina wellbore 16 that has been drilled from surface and lined withwellbore-lining tubing in the form of a metal casing 18. The casing 18typically comprises a number of sections of tubing coupled togetherend-to-end, and has been installed and cemented in the wellbore 16 usingcement 20, in a fashion which is well known in the field of theinvention. The tubing 14 carrying the packer 10 defines a tool string15, which has been run-in to the wellbore 16 to carry out a desireddownhole function or functions, optionally involving the activation of atool or tools (not shown) carried by the string. The packer 10 isemployed to seal the tubing 14 relative to an inner wall 22 of thecasing 18. This is desirable to enable the particular downholefunction(s) to be carried out, which may involve supplying a fluid fromsurface down through the tubing 14, and/or recovering fluid to surfacethrough the tubing. Migration of fluid along the wellbore 16 past thepacker 10, along an annular region 26 defined between the casing innerwall 22 and the tubing 14, is prevented following activation of thepacker.

The packer 10 is shown in FIG. 1 with the seal assembly 12 and support13 in unexpanded configurations, where the seal assembly does notcontact the inner wall 22 of the casing 18. The tubing 14 is positionedwithin the casing 18 using a dedicated tubing hanger (not shown). Thepacker 10 is set by applying ‘weight’ to the packer after the tubing 14has been set in (or ‘hung’ from) the casing 18. This is achieved byexerting an axially directed load on the seal assembly 12, to radiallyexpand it outwardly into contact with the casing inner wall 22. Theapplication of weight to set the packer 10 will be described in moredetail below.

The seal assembly 12 and support 13 are better shown in FIGS. 2 to 11.FIGS. 2 and 3 are enlarged perspective and side views of the sealassembly 12. FIG. 4 is a view which is similar to FIG. 3, but showingthe support 13 in longitudinal cross-section. FIGS. 5, 6 and 7 are viewssimilar to FIGS. 2, 3, and 4, respectively, but showing the packer 10following actuation, in which the seal assembly 12 (and so the support13) has been radially expanded. FIG. 8 is a perspective view of thesupport 13 shown prior to expansion, as in FIG. 2. FIG. 9 is aperspective view of the support 13 following expansion, as in FIG. 5.FIGS. 10 and 11 are side views of the support 13 in the configurationsof FIGS. 8 and 9, respectively.

The expandable seal assembly 12 generally comprises an expandable sealelement 30 which is radially expandable between an unexpandedconfiguration (FIG. 2), where the seal element is out of contact with adownhole surface (casing inner wall 22), and an expanded configuration(FIG. 5), where the seal element can sealingly abut the downholesurface. The seal assembly 12 also comprises the elastically deformablesupport 13, which serves for supporting the expandable seal element 30and, as will be described below, facilitates the application of force tothe seal element to radially expand it.

The support 13 is deformable between an unexpanded configuration (e.g.FIGS. 2 and 8) and a radially expanded configuration (e.g. FIGS. 5 and9). The support 13 is preferably one-piece, comprising a plurality ofbase portions which are each given the reference numeral 31, and aplurality of overlap portions (or anti extrusion members) which are eachgiven the reference numeral 35. Each base portion 31 has a surface 33which faces towards the seal element 30. Each overlap portion 35 extendsfrom a respective base portion 31 so that it overlaps the surface 33 ofan adjacent base portion 31, and has a surface 37 which also facestowards the seal element 30. By way of example, and referringparticularly to FIG. 9, a base portion 31 a is shown which has a surface33 a, and an overlap portion 35 a having a surface 37 a extends from thebase portion 31 a so that it overlaps a surface 33 b of an adjacent baseportion 31 b.

The base portions 31 and the overlap portions 35 are arranged to definea generally ring-shaped seal support structure 39 which forms acontinuous circumferentially extending support surface 41, for abuttingand supporting the seal element 30. As will be described below, thesupport surface 41 also serves for urging the seal element 30 to itsradially expanded configuration. The base portions 31 are arranged sothat they can separate to facilitate expansion of the support 13, andthe overlap portions 35 are arranged so that they can slide over thesurface 33 of the adjacent base portion during expansion of the support.In the expanded configuration of the support 13, the continuouscircumferentially extending support surface 41 comprises the surfaces 37of the overlap portions 35, and at least part of the surfaces 33 of atleast some of the base portions 31. In use, the seal element 30 isaxially compressed between the support surface 41 defined by the support13, and a shoulder 49 of an activation member 34 of the packer 10, sothat it is urged radially outwardly into contact with the casing wall22.

The deformable support 13 of the present invention provides numerousadvantages over prior supports. These include that the continuouscircumferentially extending support surface 41 restricts axial extrusionof the seal element 30 following expansion of the support 13 and theseal element 30. This means that there is no extrusion gap for the sealelement 30, which enables seal elements of existing sealing systems tooperate at substantially higher pressures, and possibly highertemperatures, or a combination of the two. Also, as the overlap portions35 extend from a respective base portion 31, the overlap portionseffectively separate when the support 13 is expanded (facilitated byseparation of the base portions). This may help to ensure that expansionof the support 13 occurs in a smooth and predictable fashion, and mayalso make the support less complex and easier to manufacture than priorsupports.

In the unexpanded configuration of the support 13, the continuouscircumferentially extending support surface 41 is defined by thesurfaces 37 of the overlap portions 35. In the expanded configuration,the support surface 41 is defined by the surfaces 37 of the overlapportions 35, and part of the surfaces 33 of all the base portions 31.Each overlap portion 35 extends in a generally circumferential directionfrom the respective base portion 31 over the surface 33 of thecircumferentially adjacent base portion 31. The generally ring-shapedsupport structure 39 comprise a radially outer extent 43, and a radiallyinner extent 45. The base portions 31 each extend across a full radialwidth of the support structure 39, and so extend from the inner extent45 to the outer extent 43. The overlap portions 35 similarly extendacross the full radial width of the support structure 39.

The base portions 31 are arranged so that they form a base section 47(FIG. 10) of the support structure 39 and, in the unexpandedconfiguration of the support 13, the base portions 31 are arranged toform a ring-shaped base section. Each base portion 31 abuts adjacentbase portions when in the unexpanded configuration; expansion of thesupport 13 causes the base portions to move out of abutment and soseparate. The overlap portions 35 similarly form an overlap section 51(FIG. 10) of the support structure 39 and, in the unexpandedconfiguration of the support 13, the overlap portions 35 are arranged toform a ring-shaped overlap section. Each overlap portion 35 abutsadjacent overlap portions when in the unexpanded configuration;expansion of the support 12 causes the overlap portions to move out ofabutment and slide over the surface 33 of the adjacent base section 31.

The support structure 39 is provided on an axial end 42 of the support13, so that the support surface 41 defined by the seal support structureis effectively a radially extending support surface which abuts andsupports an axial end 53 of the seal element 30. The base portions 31are spaced axially from the overlap portions 35, the overlap portionsbeing located closer to the seal element 30. The overlap portions 35 aretypically provided integrally with their respective base portion 31, butmay be provided as separate components which are attached to theirrespective base portion.

The base portions 31 are arranged so that they are generally in a firstplane 55 (FIG. 3) which is perpendicular to a main axis 50 of thesupport. The overlap portions 35 each extend out of the first plane 55,to overlap the surface 33 of the adjacent base portion 31. The overlapportions are arranged so that they are generally in a second plane 57which is parallel to the first plane, and spaced axially along thesupport 13 from the first plane. The second plane 57 is disposed closerto the seal element 30 than the first plane.

As best shown in FIGS. 8 and 9, the overlap portions 35 each have firstand second circumferential edges 59 and 61. An edge 59 of one overlapportion 35 abuts an edge 61 of an adjacent overlap portion 35, when thesupport 13 is in its unexpanded configuration. The overlap portions 35are arranged to taper towards the edges 59 and 61, so that the edges areeffectively tapered or chamfered. This may facilitate return movement ofthe support 13 to the unexpanded configuration, in that it may help tourge the seal element 30 from an expanded configuration back to anunexpanded configuration and/or may prevent the seal element fromrestricting return movement of support to its unexpanded configuration.Effectively, the overlap portions 35 have a thickness in an axialdirection of the support 13, and taper in thickness towards the edges 59and 61. The overlap portions 35 also taper from the outer extent 43 tothe inner extent 45, so that the first and second circumferential edges59 and 61 are inclined. Typically, the edges 59 and 61 are disposedparallel to a radius of the support 13 (at least when in its unexpandedconfiguration). The overlap portions 35 have a greater width at theouter extent 43 than at the inner extent 45, and are generallytrapezoidal, for example wedge-shaped.

The base portions 31 similarly have first and second circumferentialedges 63 and 65. An edge 63 of one base portion 31 abuts an edge 65 ofan adjacent base portion 31, when the support 13 is in its unexpandedconfiguration. The base portions 31 also taper from the outer extent 43of the support structure 39 towards the inner extent 45. Once again,this is achieved by arranging the circumferential edges 63 and 65 sothat they are inclined, and typically parallel to a radius of thesupport 13 (at least when in its unexpanded configuration). The baseportions 31 also have a greater width at the outer extent 43 than at theinner extent 45, and are similarly generally trapezoidal, for examplewedge-shaped.

The support 13 in fact comprises first and second axially opposed ends42 and 44. The generally ring-shaped seal support structure 39 isprovided on the first axial end 42, and forms a first such supportstructure. A second generally ring-shaped seal support structure 39′ isprovided on the second axial end 44. The first and second seal supportstructures 39 and 39′ are of similar structure, and so each compriserespective base portions 31 and overlap portions 35. The first sealsupport structure 39 is arranged to abut and support the seal element30, which forms a first seal element of the seal assembly 12, and whichis provided at the first axial end 42 of the support 13. The second sealsupport structure 39′ is arranged to abut and support a second sealelement 30′ at the second axial end 44 of the support 13. Advantageouslytherefore, the support 13 is capable of abutting and supporting twoseparate, axially spaced seals 30 and 30′.

The base portions 31 each comprise a pair of legs, arms or fingers 67(FIG. 9) extending in an axial direction of the support 13. The legs 67of each base portion 31 in the first seal support structure 30 eachextend to a different base portion 31 of the second seal supportstructure 30′. Similarly, the legs 67 of each base portion 31 in thesecond seal support structure 30′ each extend to a different baseportion 31 of the first seal support structure 30. This facilitatescircumferential expansion of the support 13, and effectively provides acontinuous length of material extending around the circumference of thesupport 13.

The support 13 is typically of a first material and the seal element 30of a second material having a modulus of elasticity which is less thanthat of the first material. The seal assembly 12 describes an innerdiameter, and the inner diameter of the seal assembly in the expandedconfiguration (FIG. 5) is greater than the inner diameter of the sealassembly in the unexpanded configuration (FIG. 2).

The seal assembly 12 is mounted on a main body 32 of the packer 10 (FIG.4), which is a base pipe or mandrel. The packer 10 comprises a pair ofopposed actuation members 34 and 36 which cooperate to urge the sealassembly 12 to the expanded configuration. The actuation member 34 formsan upper (or uphole) actuation member of the pair, and is moveablerelative to the packer mandrel 32, to urge the seal assembly 12 to theexpanded configuration. In a variation on the embodiment shown in thedrawings, the actuation member 36, which forms a lower (or downhole)actuation member, may be movable relative to the mandrel 32 to urge theseal assembly 12 to the expanded configuration. In a further variation,both actuation members 34 and 36 may be movable relative to the mandrel32. The seal assembly 12 is expanded by translating the upper actuationmember 34 axially towards the lower actuation member 36. This imparts anaxially directed expansion force on the seal assembly 12, to urge theseal elements 30 and 30′ radially outwardly to seal against the casinginner wall 22.

The support 13 comprises at least one load surface and, in theillustrated embodiment, comprises two such load surfaces 38 and 40 atthe respective first and second axial ends 42 and 44. The load surfaces38 and 40 are shaped to cooperate with corresponding load/expansionsurfaces 46 and 48 on the respective actuation members 34 and 36, formoving the support 13, and so the seal assembly 12, to the expandedconfiguration. As can be seen from the drawings, the load surfaces 38and 40 of the seal assembly 12 are inclined relative to the longitudinalaxis 50 of the support 13. The load surfaces 46 and 48 on the packeractuation members 34 and 36 are oppositely inclined, so that axialmovement of the upper actuation member 34 acts to urge the support 13radially outwardly. The load surfaces 46 and 48, together with thesupport 13, act to bring the seal elements 30 and 30′ into contact withthe casing inner wall 22. The load surfaces 38 and 40 of the sealassembly 12 are effectively tapered, and extend in axially inwarddirections from the respective ends 42 and 44. The load surfaces 38 and40 incline in such a way that the inner diameter described by the loadsurfaces decrease in a direction along the assembly 12 from therespective end 42, 44.

As can be seen from FIGS. 4 and 7, movement of the support 13 to theexpanded configuration causes the inner diameter of the support toincrease, the inner diameter of the seal assembly 12 in the expandedconfiguration being greater than that in the unexpanded configuration.This effectively provides a radial spacing or gap (FIG. 7) between aninner surface 52 of the support 13 and an outer surface 54 of the packermandrel 32, when the support is moved to the expanded configuration.This facilitates contraction of the seal assembly 12 back to theunexpanded configuration, and so removal of the seal assembly from thewellbore 16. This is further facilitated by providing the support 13 asan elastically deformable component; the support 13 returns to theunexpanded configuration in the absence of an applied expansion force.

The structure and performance of the seal assembly 12 during operationwill now be described in more detail. As can be seen from FIGS. 2 and 3,the support 13 is arranged so that it deforms uniformly. The support 13describes an inner diameter which is uniform along a main length when itis in the expanded configuration, and also in the unexpandedconfiguration. The support 13 is tubular and particularly is generallyannular in shape, and configured so that it circumferentially expandswhen the seal assembly 12 is moved to the expanded configuration. Thesupport 13 comprises a plurality of slots, channels or the like,designated by numerals 56 and 58. Each slot 56, 58 extends between innerand outer surfaces 60, 62 of the component 28, and so extends entirelythrough a wall 64 of the component. The slots 56 and 58 also extend inan axial direction along the support 13 from the respective axial ends42 and 44, and are positioned so that their respective main axes 66 and68 are disposed generally parallel to the main longitudinal axis 50, inthe unexpanded configuration.

The support 13 actually comprises a first set of the slots 56, each ofwhich extends inwardly from the first axial end 42, and a second set ofthe slots 58, each of which extends inwardly from the second axial end44. The slots 56 and 58 are alternately circumferentially spaced aroundthe circumference of the support 13. The slots 56, 58 open when a forceis exerted on the seal assembly 12, and so the support 13, to move it tothe expanded configuration, and each have a circumferential width whichincreases when the seal assembly is moved to the expanded configuration.The support 13 therefore circumferentially expands when it is moved tothe expanded configuration. Main parts of the slots 56 and 58 have awidth which is substantially constant when the support 13 is in theunexpanded configuration, and the slots are arranged so that, onexpansion, the width increases and is then non-constant in a directionalong at least said main parts. The slots 56 and 58 extend from theaxial ends 42, 44 of the support 13, the ends of the slots here beingdefined between adjacent base portions 31. The slots 56 and 58 definerespective expansion nodes 80 and 82 at their opposite ends.

The slots 56 each have opposed sidewalls 84 which extend from therespective node 80, and the slots 58 similarly each have opposedsidewalls 86 which extend from the respective node 82. Expansion occursby at least part of each of said slot sidewalls 84, 86 pivoting ordeflecting about the respective nodes 80, 82. The sidewalls 84, 86 pivotor deflect in a scissors-fashion about the nodes 80 and 82, the nodeseffectively forming roots of the slots 56, 58 with expansion occurringby pivoting/deflecting of said part of the sidewalls 84, 86 from theroot so that the sidewalls diverge in a direction away from the root.Each node 80, 82 has a respective wall which is curved, and whichoptionally has a substantially constant radius of curvature, the nodewalls communicating with the slot or channel sidewalls 84, 86. Providinga node wall which has such a substantially constant radius of curvatureresults in the node being generally circular, which can reduce stressconcentrations in the support 13 under load.

The support 13 is typically of a metal, metal alloy or plasticsmaterials. The seal elements 30 and 30′ are typically of an elastomericor rubber material, the material selected having a modulus of elasticitywhich results in the seal elements 30, 30′ exerting a restorative forcewhich tends to urge the seal assembly 12 towards the unexpandedconfiguration, when an expansion force is removed. Typical moduli ofelasticity for the material of the support 13 are in the range of around180 GPa to around 200 GPa. Typical moduli of elasticity for the materialof the seal elements 30, 30′ are in the range of around 0.01 GPa toaround 0.1 GPa. The support 13 is typically formed by machining atubular body to form the required slots 56, 58.

As discussed above, movement of the seal assembly 12 to the expandedconfiguration provides a seal against the casing inner wall 22, therebysealing the annular region 26. Expansion is achieved by urging thepacker actuation member 34 axially downwardly (or downhole), towards theopposed actuation member 36, by imparting the necessary ‘weight’ on theactivation member 34 from surface or via a component of the packer 10 ora tool coupled to the packer, in a known fashion. This causes the loadfaces 38 and 40 of the support 13 to travel along the load faces 46 and48 of the actuation members 34 and 36, thereby radially andcircumferentially expanding the support. This results in radialexpansion of the seal elements 30 and 30′, which are axially compressedbetween the support surfaces 41 and 41′ defined by the support 13,shoulders 49 and 49′ of the activation members 34 and 36.

This movement continues until the seal elements 30 and 30′ are broughtinto contact with the casing inner wall 22, whereupon further axialforce on the seal assembly 12 imparts a radially directed sealing forceon the seal elements 30 and 30′, compressing them against the casinginner wall 22. A desired axial setting force is applied to the packer10, to ensure an adequate radial load on the seal elements 30 and 30′,and so seal with the casing wall 22. The packer 10 has then been fullyset, and provides a sufficient seal to ensure that fluid cannot migratealong the wellbore 16 past the packer. The desired downhole function orfunctions can then be carried out, employing the tool or tools carriedby the string 15.

When it is desired to deactivate the packer 10, for example followingcompletion of the desired downhole function(s), the activation member 34is axially translated back along the packer mandrel 32 towards the startposition (FIG. 2). The inherent elasticity of the support 13 tends toreturn it to the unexpanded configuration (FIG. 2). This may also befacilitated by the seal elements 30 and 30′, which may have sufficientelasticity that they assist in movement of the support 13 back to theunexpanded configuration. The tool string 15 comprising the packer 10and tubing 14 can then be pulled out of the wellbore 16, if required.

Turning now to FIG. 12, there is shown a side view of downhole tool, inthe form of a packer or bridge plug 10 a, comprising at least oneexpandable seal assembly 12 a incorporating an elastically deformablesupport 13 a for an expandable seal element 30 a of the assembly,according to another embodiment of the invention. Like components of theassembly 12 a with the assembly 12 of FIGS. 1 to 11 share the samereference numerals, with the addition of the suffix ‘a’.

The assembly 12 a in fact comprises two expandable seal elements 30 aand 30 a′, although as with the assembly 12, there may be a single sealelement, and indeed two of the supports 13 a for a single seal elementlocated between the supports.

The only substantial difference between the assembly 12 a and theassembly 12 is that actuation members 34 a and 34 a′ are provided whichcomprise respective seal expansion surfaces 46 a, 46 a′ arranged to urgethe seal elements 30 a, 30 a′ to their expanded configuration, andsupport expansion surfaces 100 and 100′ arranged to urge the supportelement 13 a to its expanded configuration. The expansion surfaces areall inclined relative to a main axis of the tool 10 a, and the expansionsurfaces 100, 100′ optionally have a steeper inclination than theexpansion surfaces 46 a, 46 a′. In this way, the support element 13 a isurged outwardly to its expanded configuration ahead of the seal elements30 a, 30 a′ to ensure adequate support for the seal elements 30 a. 30 a′under load (helping to resist unwanted axial extrusion).

FIG. 13 is a side view of an elastically deformable support 13 baccording to a further embodiment of the invention, which has a use inany of the assemblies disclosed herein. Like components of the support13 b with the support 13 of FIGS. 1 to 11 share the same referencenumerals, with the addition of the suffix ‘b’.

In this embodiment, a seal element 30 b is mountable on or in a supportsurface 41 b of the support 13 b, so that the support effectively has anintegral seal element which is radially and circumferentially expandedwhen the support is expanded. The seal element 30 b is an annular sealelement such as an O-ring (of any suitable cross-section anddimensions), and is located in a seat 102, which takes the form of anannular groove or recess in the support surface 41 b. It will beunderstood that the seat 102 may be defined mainly by overlap portions35 b of the support 13 b, and that part of the seal element 30 b mayrest upon surfaces of base portions 31 b when the support 13 b is in anexpanded configuration. The seat 102 may effectively be provided at aradially outer peripheries of the overlap portions 35 b. The supportelement 13 b may effectively define a retractable seal seat, actuated bymovement of the support between its unexpanded and expandedconfigurations.

In a variation, the seal element 30 b may be bonded on to parts orprotrusions (not shown) of the overlap portions 35 b, or may just reston an extended “ledge” defined by the overlap portions, but in each caseis expanded and brought into sealing contact with the downhole surfaceat the same time as and along with the expansion of the support.

Whilst FIG. 13 shows only a single such annular seal element 30 b, itwill be understood that a similar such seal element (not shown) may beprovided on or in a support surface 41 b′ defined at the other end ofthe support element 13 b.

FIGS. 14 and 15 are enlarged side and end views, respectively, of partof an elastically deformable support 13 c according to a still furtherembodiment of the invention, which has a use in any of the assembliesdisclosed herein. Like components of the support 13 c with the support13 of FIGS. 1 to 11 share the same reference numerals, with the additionof the suffix ‘c’.

The support 13 c defines a continuous circumferentially extendingsupport surface 41 c for abutting and supporting a radially innersurface of a seal element (not shown). A generally ring-shaped sealsupport structure 39 c is thus provided which is on/defines a radiallyouter surface 104 of the support 13 c. This is achieved by providingoverlap portions 35 c which extend in a radially outward direction fromrespective base portions 31 c.

The support 13 c shown in this embodiment can be arranged so that it iseffectively a variation on the support 13 b of FIG. 13. This can beachieved by providing a seal element 30 c, which is mountable on or inthe support surface 41 c, so that the support 13 c effectively has anintegral seal element. The seal element 30 c is provided on or in aradially outer surface of the support 13 c. Once again, the seal element30 c is an annular seal element such as an O-ring, and is located in aseat 102 c, which takes the form of an annular groove or recess in thesupport surface 41 c. The seat 102 c is defined by overlap portions 35 cof the support 30 c, part of the seal element 30 c resting upon surfacesof base portions 31 c when the support 30 c is in an expandedconfiguration.

The supports 13 b/13 c could have uses where a certain component needsto pass and seal through a second component which has a restrictionprior to a sealing area, which might be of a larger diameter. There area variety of sealing systems available, which could utilise the presentinvention as a back-up/support.

The supports disclosed herein may be ‘high expansion’, and so highexpansion supports. This may have a use where a tool of a certaindiameter is to pass a restriction, and then to expand into a largerdiameter area whilst sealing pressure from above and below. Such mayinvolve a temporary (and so retractable) or permanent deployment. Thedisclosed expandable seal assemblies and hence seal elements maysimilarly be high expansion assemblies/elements. A ratio of an outerdiameter of the support/seal element in the unexpanded configurationrelative to an outer diameter in the expanded configuration may be atleast about 1:1.2 (representing at least a 20% expansion).

Various modifications may be made to the foregoing without departingfrom the spirit or scope of the present invention.

An expandable seal assembly may be provided comprising first and secondsupports of the type described herein, and a seal element disposedbetween the supports so that the first support abuts and supports afirst surface of the seal element and the second support abuts andsupports a second surface of the seal element. Effectively, the assemblyof the present invention may be operable with one or more seal elementsusing one or more supports.

The support may define a gripping arrangement, which may be for grippinga downhole surface. This may enable the support to act as a slip or setof slips. The gripping arrangement may be provided on or defined by aradially outer surface of the support. The gripping arrangement maycomprise a plurality of gripping elements, which may be protrusions suchas teeth. The gripping arrangement may be provided by arranging at leastpart of said outer surface to be roughened, and/or by applying a coatingto the part of said surface which is of a higher coefficient of frictionthan a material of the support (for example, a Tungsten Carbidecoating).

The support may comprise a seal component extending around at least partof a radially outer surface of the support. The seal component may be agenerally tubular sheath. Where the support comprises a plurality ofslots, the seal component may extend at least partly into the slots. Thesupport may be encapsulated by the seal component. This may provide theadvantages of: reducing junk ingress to the slots, causing it to notretract fully;

and aiding return to the unexpanded configuration (i.e. to gauge OD) byincreasing the ‘memory’ of the support.

In the unexpanded configuration of the support, the continuouscircumferentially extending support surface may comprise or may definethe surfaces of the overlap portions and at least part of the surfacesof at least some of the base portions. In this case, in the expandedconfiguration of the support, the continuous circumferentially extendingsupport surface may comprise the surfaces of the overlap portions and agreater proportion of the surfaces of said base portions than in theunexpanded configuration.

At least one of the overlap portions may overlap the surface of morethan one adjacent base portion. At least one of the overlap portions mayextend from the respective base portion in opposed first and seconddirections, so that it overlaps base portions located adjacent first andsecond sides of the base portion from which the overlap portion extends.

At least one of the overlap portions may extend across and overlap theentire surface of the adjacent base portion, and over a surface of afurther base portion.

1. A one-piece elastically deformable support for an expandable sealelement of a downhole tool, in which the support is deformable betweenan unexpanded configuration and a radially expanded configuration andcomprises: a plurality of base portions, each base portion having asurface which, in use, faces towards the seal element; and a pluralityof overlap portions, each overlap portion extending from a respectivebase portion so that it overlaps the surface of an adjacent base portionand having a surface which, in use, faces towards the seal element; inwhich the base portions and the overlap portions are arranged to definea generally ring-shaped seal support structure which forms a continuouscircumferentially extending support surface for abutting and supportingthe seal element.
 2. A support as claimed in claim 1, in which: the baseportions are arranged so that they can separate to facilitate expansionof the support; the overlap portions are arranged so that they can slideover the surface of the adjacent base portion during expansion of thesupport; and in the expanded configuration of the support, thecontinuous circumferentially extending support surface comprise thesurfaces of the overlap portions and at least part of the surfaces of atleast some of the base portions.
 3. A support as claimed in claim 1 inwhich, in the unexpanded configuration of the support, the continuouscircumferentially extending support surface is defined by the surfacesof the overlap portions.
 4. A support as claimed in claim 1 in which, inthe unexpanded configuration of the support, the continuouscircumferentially extending support surface is defined by the surfacesof the overlap portions and at least part of the surfaces of at leastsome of the base portions.
 5. A support as claimed in claim 1 in which,the expanded configuration, the continuous circumferentially extendingsupport surface comprises the surfaces of the overlap portions and atleast part of the surfaces of the base portions.
 6. A support as claimedin claim 1, in which each overlap portion extends in a generallycircumferential direction from the respective base portion over thesurface of the adjacent base portion.
 7. A support as claimed in claim1, in which the generally ring-shaped support structure comprise aradially outer extent and a radially inner extent, and in which the baseportions each extend across a full radial width of the supportstructure, and so from the inner extent to the outer extent.
 8. Asupport as claimed in claim 1, in which the generally ring-shapedsupport structure comprise a radially outer extent and a radially innerextent, and in which the overlap portions each extend across a fullradial width of the support structure, and so from the inner extent tothe outer extent.
 9. A support as claimed in claim 1, in which the baseportions form a ring-shaped base section of the generally ring-shapedseal support structure, when the support is in the unexpandedconfiguration.
 10. A support as claimed in claim 1, in which the overlapportions form a ring-shaped overlap section of the generally ring-shapedseal support structure, when the support is in the unexpandedconfiguration.
 11. A support as claimed in claim 1, in which the supportsurface is for abutting and supporting an axial end of the seal element,the generally ring-shaped seal support structure defining an axial endof the support.
 12. A support as claimed in claim 1, in which the baseportions are spaced axially from the overlap portions so that, in use,the overlap portions are located closer to the seal element than thebase portions.
 13. A support as claimed in claim 1, in which the baseportions are arranged so that they are generally in a first plane whichis perpendicular to a main axis of the support, and in which the overlapportions each extend out of the first plane to overlap the surface ofthe adjacent base portion.
 14. A support as claimed in claim 13, inwhich the overlap portions are arranged so that they are generally in asecond plane which is parallel to the first plane, and spaced axiallyalong the support from the first plane.
 15. A support as claimed inclaim 1, in which the overlap portions have first and secondcircumferential edges, and in which the overlap portions are arranged totaper in axial thickness towards the edges.
 16. A support as claimed inclaim 1, in which the base portions and the overlap portions haveradially outer and radially inner extents, and have a greater width attheir outer extents than at their inner extents.
 17. A support asclaimed in claim 1, comprising: first and second axially opposed ends; afirst generally ring-shaped seal support structure provided on the firstaxial end; and a second generally ring-shaped seal support structureprovided on the second axial end; in which the first generallyring-shaped seal support structure is arranged to abut and support afirst seal element at the first axial end of the support, and the secondgenerally ring-shaped seal support structure is arranged to abut andsupport a second seal element at the second axial end of the support.18. A support as claimed in claim 17, in which the base portions eachcomprise a plurality of legs extending in an axial direction of thesupport, each leg of each base portion extending to a different baseportion on the other seal support structure.
 19. A support as claimed inclaim 1, in which the support comprises a plurality of slots extendingbetween an inner surface of the support and an outer surface of thesupport and in an axial direction along the support, the slots beingexpandable to facilitate expansion of the support.
 20. A support asclaimed in claim 19, in which the seal support structure covers ends ofthe slots, to prevent extrusion of the seal element into the slotsfollowing expansion.
 21. A support as claimed in claim 19, in which thesupport comprises first and second sets of slots, each set comprising aplurality of slots, said slots of the first set extending inwardly froma first axial end of the support, and said slots of the second setextending inwardly from a second axial end of the support opposite tothe first end.
 22. A support as claimed in claim 1, comprising a sealcomponent extending around at least part of a radially outer surface ofthe support.
 23. A support as claimed in claim 1, in which the supporthas an integral seal element.
 24. A support as claimed in claim 23, inwhich the seal element is an annular seal element located in a seatdefined in the support surface.
 25. A support as claimed in claim 1, inwhich the support is a high expansion support, capable of elasticallydeforming so that a ratio of an outer diameter of the support in theunexpanded configuration relative to an outer diameter in the expandedconfiguration is at least about 1:1.20.
 26. An expandable seal assemblyfor a downhole tool, the seal assembly comprising: an expandable sealelement which is radially expandable between an unexpanded configurationwhere the seal element is out of contact with a downhole surface, and anexpanded configuration where the seal element can sealingly abut thedownhole surface; and a one-piece elastically deformable support, inwhich the support is deformable between an unexpanded configuration anda radially expanded configuration and comprises: a plurality of baseportions, each base portion having a surface which, in use, facestowards the seal element; and a plurality of overlap portions, eachoverlap portion extending from a respective base portion such that itoverlaps the surface of an adjacent base portion and having a surfacewhich, in use, faces towards the seal element; in which the baseportions and the overlap portions are arranged to define a generallyring-shaped seal support structure which forms a continuouscircumferentially extending support surface for abutting and supportingthe seal element.
 27. An assembly as claimed in claim 26, comprisingfirst and second expandable seal elements, and in which the supportcomprises first and second axially opposed ends, a first generallyring-shaped seal support structure provided on the first axial end andarranged to abut and support the first seal element, and a secondgenerally ring-shaped seal support structure provided on the secondaxial end and arranged to abut and support the second seal element. 28.An assembly as claimed in claim 26, comprising first and second suchone-piece elastically deformable supports, the seal element disposedbetween the supports so that the first support abuts and supports afirst surface of the seal element, and the second support abuts andsupports a second, opposite surface of the seal element.
 29. A downholetool comprising at least one expandable seal assembly according to claim26.
 30. An elastically deformable support for an expandable seal elementof a downhole tool, in which the support is deformable between anunexpanded configuration and a radially expanded configuration andcomprises: a plurality of base portions, each base portion having asurface which, in use, faces towards the seal element; and a pluralityof overlap portions, each overlap portion extending from a respectivebase portion so that it overlaps the surface of an adjacent base portionand having a surface which, in use, faces towards the seal element; inwhich the base portions and the overlap portions are arranged to definea generally ring-shaped seal support structure which forms a continuouscircumferentially extending support surface for abutting and supportingthe seal element; in which the base portions are arranged so that theycan separate to facilitate expansion of the support; in which theoverlap portions are arranged so that they can slide over the surface ofthe adjacent base portion during expansion of the support; and in which,in the expanded configuration of the support, the continuouscircumferentially extending support surface comprises the surfaces ofthe overlap portions and at least part of the surfaces of at least someof the base portions.